/*
 * Created on 2005-4-22
 *
 * @author xuji
 * 
 * Copyright (C) 2005, HC SOFT.
 */

package com.pingansec.utils;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

/**
 * Base64编解码实现。
 * 
 * <p>
 * 将原先使用的Apache项目中的base64类换为Bouncy Castle(www.bouncycastle.org)中的类
 *      Bouncy Castle对byte[]数据的编解码速度比原先的类稍好一点点，并直接提供了String->byte[]
 * 的decode支持，对于带回车符的字符串，如果用原先的类+StringUtil.replaceAll实现相同功能，
 * 速度提高了10倍，即使用jdk1.4 String.replaceAll，速度也提高了3倍。
 * 
 * <p>
 * 另外修正了忽略字符时的bug。
 * 
 * @author xuji
 * @version 0.9
 * @since 0.9
 */
public class Base64
{
    private static final byte[] encodingTable =
    {
        (byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G',
        (byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N',
        (byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U',
        (byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z',
        (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g',
        (byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n',
        (byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u',
        (byte)'v', (byte)'w', (byte)'x', (byte)'y', (byte)'z',
        (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6', (byte)'7', (byte)'8', (byte)'9',
        (byte)'+', (byte)'/'
    };

    /**
     * encode the input data producing a base 64 encoded byte array.
     *
     * @return a byte array containing the base 64 encoded data.
     */
    public static byte[] encode(byte[]  data)
    {
        byte[]  bytes;
        
        int modulus = data.length % 3;
        if (modulus == 0)
        {
            bytes = new byte[4 * data.length / 3];
        }
        else
        {
            bytes = new byte[4 * ((data.length / 3) + 1)];
        }

        int dataLength = (data.length - modulus);
        int a1, a2, a3;
        for (int i = 0, j = 0; i < dataLength; i += 3, j += 4)
        {
            a1 = data[i] & 0xff;
            a2 = data[i + 1] & 0xff;
            a3 = data[i + 2] & 0xff;

            bytes[j] = encodingTable[(a1 >>> 2) & 0x3f];
            bytes[j + 1] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f];
            bytes[j + 2] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f];
            bytes[j + 3] = encodingTable[a3 & 0x3f];
        }

        /*
         * process the tail end.
         */
        int b1, b2, b3;
        int d1, d2;

        switch (modulus)
        {
        case 0:     /* nothing left to do */
            break;
        case 1:
            d1 = data[data.length - 1] & 0xff;
            b1 = (d1 >>> 2) & 0x3f;
            b2 = (d1 << 4) & 0x3f;

            bytes[bytes.length - 4] = encodingTable[b1];
            bytes[bytes.length - 3] = encodingTable[b2];
            bytes[bytes.length - 2] = (byte)'=';
            bytes[bytes.length - 1] = (byte)'=';
            break;
        case 2:
            d1 = data[data.length - 2] & 0xff;
            d2 = data[data.length - 1] & 0xff;

            b1 = (d1 >>> 2) & 0x3f;
            b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;
            b3 = (d2 << 2) & 0x3f;

            bytes[bytes.length - 4] = encodingTable[b1];
            bytes[bytes.length - 3] = encodingTable[b2];
            bytes[bytes.length - 2] = encodingTable[b3];
            bytes[bytes.length - 1] = (byte)'=';
            break;
        }

        return bytes;
    }

    /*
     * set up the decoding table.
     */
    private static final byte[] decodingTable;

    static
    {
        decodingTable = new byte[128];

        for (int i = 'A'; i <= 'Z'; i++)
        {
            decodingTable[i] = (byte)(i - 'A');
        }

        for (int i = 'a'; i <= 'z'; i++)
        {
            decodingTable[i] = (byte)(i - 'a' + 26);
        }

        for (int i = '0'; i <= '9'; i++)
        {
            decodingTable[i] = (byte)(i - '0' + 52);
        }

        decodingTable['+'] = 62;
        decodingTable['/'] = 63;
    }

    /**
     * decode the base 64 encoded input data. It is assumed the input data is valid.
     *
     * @return a byte array representing the decoded data.
     */
    public static byte[] decode(byte[]  data)
    {
        byte[]  bytes;
        byte    b1, b2, b3, b4;

        if (data[data.length - 2] == '=')
        {
            bytes = new byte[(((data.length / 4) - 1) * 3) + 1];
        }
        else if (data[data.length - 1] == '=')
        {
            bytes = new byte[(((data.length / 4) - 1) * 3) + 2];
        }
        else
        {
            bytes = new byte[((data.length / 4) * 3)];
        }

        for (int i = 0, j = 0; i < data.length - 4; i += 4, j += 3)
        {
            b1 = decodingTable[data[i]];
            b2 = decodingTable[data[i + 1]];
            b3 = decodingTable[data[i + 2]];
            b4 = decodingTable[data[i + 3]];

            bytes[j] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[j + 1] = (byte)((b2 << 4) | (b3 >> 2));
            bytes[j + 2] = (byte)((b3 << 6) | b4);
        }

        if (data[data.length - 2] == '=')
        {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];

            bytes[bytes.length - 1] = (byte)((b1 << 2) | (b2 >> 4));
        }
        else if (data[data.length - 1] == '=')
        {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            b3 = decodingTable[data[data.length - 2]];

            bytes[bytes.length - 2] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 1] = (byte)((b2 << 4) | (b3 >> 2));
        }
        else
        {
            b1 = decodingTable[data[data.length - 4]];
            b2 = decodingTable[data[data.length - 3]];
            b3 = decodingTable[data[data.length - 2]];
            b4 = decodingTable[data[data.length - 1]];

            bytes[bytes.length - 3] = (byte)((b1 << 2) | (b2 >> 4));
            bytes[bytes.length - 2] = (byte)((b2 << 4) | (b3 >> 2));
            bytes[bytes.length - 1] = (byte)((b3 << 6) | b4);
        }

        return bytes;
    }

    private static boolean ignore(char c)
    {
        return (c == '\n' || c =='\r' || c == '\t' || c == ' ');
    }
    
    /**
     * decode the base 64 encoded String data - whitespace will be ignored.
     *
     * @return a byte array representing the decoded data.
     */
    public static byte[] decode(String data)
    {
        ByteArrayOutputStream   bOut = new ByteArrayOutputStream();
        
        try
        {
            decode(data, bOut);
        }
        catch (IOException e)
        {
            throw new RuntimeException("exception decoding base64 string: " + e);
        }
        
        return bOut.toByteArray();
    }
    
    /**
     * decode the base 64 encoded String data writing it to the given output stream,
     * whitespace characters will be ignored.
     *
     * @return the number of bytes produced.
     */
    public static int decode(String data, OutputStream out) throws IOException
    {
        byte    b1, b2, b3, b4;
        int     length = 0;
        
        int     end = data.length();
        
        while (end > 0)
        {
            if (!ignore(data.charAt(end - 1)))
            {
                break;
            }
            
            end--;
        }
        
        /*
        for (int i = 0; i < end - 4; i += 4)
        {
            if (ignore(data.charAt(i)))
            {
                continue;
            }
            
            b1 = decodingTable[data.charAt(i)];
            b2 = decodingTable[data.charAt(i + 1)];
            b3 = decodingTable[data.charAt(i + 2)];
            b4 = decodingTable[data.charAt(i + 3)];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            out.write((b3 << 6) | b4);
            
            length += 3;
        }
        */
        // 2006-3-11 renw fix bug: 忽略字符时不能跳过4个
        int i = 0;
        while (i < end - 4) {
            if (ignore(data.charAt(i)))
            {
                i++;
                continue;
            }
            
            b1 = decodingTable[data.charAt(i)];
            b2 = decodingTable[data.charAt(i + 1)];
            b3 = decodingTable[data.charAt(i + 2)];
            b4 = decodingTable[data.charAt(i + 3)];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            out.write((b3 << 6) | b4);
            
            length += 3;
            i += 4;
        }

        if (data.charAt(end - 2) == '=')
        {
            b1 = decodingTable[data.charAt(end - 4)];
            b2 = decodingTable[data.charAt(end - 3)];

            out.write((b1 << 2) | (b2 >> 4));
            
            length += 1;
        }
        else if (data.charAt(end - 1) == '=')
        {
            b1 = decodingTable[data.charAt(end - 4)];
            b2 = decodingTable[data.charAt(end - 3)];
            b3 = decodingTable[data.charAt(end - 2)];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            
            length += 2;
        }
        else
        {
            b1 = decodingTable[data.charAt(end - 4)];
            b2 = decodingTable[data.charAt(end - 3)];
            b3 = decodingTable[data.charAt(end - 2)];
            b4 = decodingTable[data.charAt(end - 1)];

            out.write((b1 << 2) | (b2 >> 4));
            out.write((b2 << 4) | (b3 >> 2));
            out.write((b3 << 6) | b4);
            
            length += 3;
        }

        return length;
    }
}
